• Conservation, sources d'inoculum
  

Thanks to its mycelium, sclerotia and conidia, Passalora fulva is preserved on and in the ground , on the walls of shelters. Its saprophytic potential allows it to also maintain itself on plant debris. Very resistant to desiccation, its conidia can survive in a greenhouse for more than a year in the absence of a sensitive host. This fungus can also persist on seeds . Note that it has been described in Brazil on Carica papaya , a host likely to perpetuate it.

• Penetration and invasion

On coming into contact with the leaves, conidia germinate if a film of water is present or if the humidity is greater than 85%. P. fulva enters the leaves through the stomata . The contamination is done in 24 to 48 hours in poorly ventilated shelters. The mycelium invades the intercellular spaces of the mesophyll. The incubation is long: it usually lasts 10 to 15 days and sporulation occurs within hours.

• Sporulation and dissemination

Once produced in large numbers on conidiophores (figure 1) on the underside of leaflets, conidia (photos 1 and 2) are easily dispersed by wind , drafts in shelters, splashing water , tools, workers' clothes. Certain insects would also ensure the dissemination of this fungus. The higher the humidity, the greater the sporulation.

• Conditions favorable to its development

In Europe, P. fulva is typically a parasitic fungus of crops under cover where high humidity prevails. It is most prevalent in the fall and early winter, and in the spring. In these shelters, the day / night climatic contrasts are very favorable, as well as the overcast and not very bright weather. It is sometimes found in the open, in the shade of hedges and when conditions are wet. It particularly likes temperatures of around 20 to 25 ° C and humid environments , and its activity is limited below 11 ° C. In tropical areas, it occurs especially during “cool” periods, when the air humidity is high. Excessive nitrogen fertilization also promotes leaf blight.